Many portable electronic devices include one or more rechargeable batteries that require external power to recharge from time to time. Such devices may include cell phones, smart phones, tablet computers, laptop computers, wearable devices, navigation devices, sports devices, health devices, medical devices, accessory devices, peripheral input devices, and so on.
Some electronic devices may include an inductive charging system in lieu of a cable or tethered charging system. In these examples, a user may place the portable electronic device on an inductive charging surface (“dock”) to replenish a rechargeable battery via electromagnetic induction. In these systems, an electromagnetic coil (“transmit coil”) within the dock may inductively couple to an electromagnetic coil (“receive coil”) within the portable electronic device. By alternating or switching the current through the transmit coil, current may be induced in the receive coil. The portable electronic device may be adapted to use the received current to replenish the charge of a rechargeable battery.
Many portable electronic devices may enter multiple power modes during an inductive power transfer. For example, a portable electronic device with a rechargeable battery may switch, after a period of time, from a trickle charging mode drawing low power to a constant current charging mode drawing relatively high power. Each of the several operational modes may present a different load condition as seen by the inductive power transmitter. In many cases, changing load conditions decreases efficiency of power transfer between the transmitter and receiver.
Accordingly, there may be a present need for a system and method for efficiently and rapidly delivering useful power to a portable electronic device across multiple power modes.